Array Expander help: Expander only shows address

[solemnservant]

While I did find other examples on this board none of them seemed to address my issue.

The problems asks to create a new array twice the size of the original. the new elements should hold zero upon completion. I seemed to work through the problem ok. My issue is the duplicated array is displaying the memory address and not the contents. I cannot figure out why that is.

Here is what I have:

//This Program will create a new array 
//that will be twice the size of the original.

# include <iostream>
using namespace std;

//Function prototypes
void displayArray(const int [], int);		//displays original array and expanded array
int *duplicateArray(const int * , int);		//duplicates original array and doubles amount of elements

/***************
Main function
***************/
int main ()
{
	const int SIZE = 10;

	int array[SIZE] = {10, 20, 30, 40, 50,		//orignal Array holds 10 elements
					   60, 70, 80, 90, 100,};

	int *dupArray;		//defines the pointer to duplicated array

	dupArray = duplicateArray(array, SIZE);

	//displays original array
	cout<< "Here are the original array's elements:\n ";
	displayArray(array, SIZE);

	//displays duplicated array with double the elements
	cout << "Here is the new duplicated array with double ";
	cout << "The amount of elements.\n :";
	displayArray(dupArray, (SIZE *2));
	
	delete [] dupArray;		//frees allocated memory and sets dupArray to zero
	dupArray = 0;


	cout <<" Press [Enter] to continue..."
	//ignores 10000 chars in keyboard buffer
	cin.ignore(10000, '\n');
	//program closes after user presses enter
	cin.get();

	return 0;
}

/*********************************************************
duplicateArray function doubles the size of the
original array and places a zero in the empty elements
*********************************************************/
int *duplicateArray (const int *arr, int size) 
{
	//Creates dynamic allocated memory space for array newArray
	int *newArray = new int [(size * 2)];

	//Validates that newArray's size will return null if
	//zero or a negative was passed
	if ((size *2) <= 0)
		return NULL;

	//duplicates the contents of the original array into newArray
	for (int dupElem = 0; dupElem < (size); dupElem++)
	{
		newArray[dupElem] = arr[size];

		while (newArray[10] < newArray[19])		//new elements are assigned zero
			newArray[dupElem] = 0;
		
	}

	//Returns pointer to the new array
	return newArray;
}

/*******************************************
Function displayArray displays original and 
duplicated array elements
********************************************/
void displayArray (const int arr [], int size)
{
	for (int index = 0; index < size; index++)
		cout << arr[index] << " ";
		cout << endl;
}

can anyone help me out?

[Zaita]

The problem is not in displaying it but your duplication code.

for (int dupElem = 0; dupElem < size; dupElem++) {
 newArray[dupElem] = arr[size]; // broken assigns invalid memory to every element 

 while (newArray[10] < newArray[19]) // This makes no sense at all
  newArray[dupElem] = 0; 
}

You want something like:

for (unsigned i = 0; i < size; ++i) {
 if (i < size)
  newArray[i] = arr[i];
 else
  newArray[i] = 0;
}

[booradley60]

Your duplicateArray function has some errors in it. First, I would make the loop that copies the existing elements over and the loop that zeroes out the new elements separate. (Don't nest one in the other.) Also, line 65 is wrong. You're accessing arr[size] which is actually one element past the end of the array! I think you mean to do this:

//duplicates the contents of the original array into newArray
    for (int dupElem = 0; dupElem < (size); dupElem++)
    {
        newArray[dupElem] = arr[dupElem];
    }

[solemnservant]

OK I looked over it again. It appears I didn't need the if/else statements either to make the program work, just two for loops. here is what I got now:

//This Program will create a new array 
//that will be twice the size of the original.

# include <iostream>
using namespace std;

//Function prototypes
void displayArray(int [], int);		//displays original array and expanded array
int *duplicateArray(int * , int);		//duplicates original array and doubles amount of elements

/***************
Main function
***************/
int main ()
{
	const int SIZE = 10;

	int array[SIZE] = {10, 20, 30, 40, 50,		//orignal Array holds 10 elements
					   60, 70, 80, 90, 100,};

	int *dupArray;		//defines the pointer to duplicated array

	dupArray = duplicateArray(array, SIZE);

	//displays original array
	cout<< "Here are the original array's elements:\n ";
	displayArray(array, SIZE);

	//displays duplicated array with double the elements
	cout << "Here is the new duplicated array with double ";
	cout << "the amount of elements:\n ";
	displayArray(dupArray, (SIZE *2));
	
	delete [] dupArray;		//frees allocated memory and sets dupArray to zero
	dupArray = 0;

	cout <<" Press [Enter] to continue...";
	//ignores 10000 chars in keyboard buffer
	cin.ignore(10000, '\n');
	//program closes after user presses enter
	cin.get();

	return 0;
}

/*********************************************************
duplicateArray function doubles the size of the
original array and places a zero in the empty elements
*********************************************************/
int *duplicateArray (int *arr, int size) 
{
	//Creates dynamic allocated memory space for array newArray
	int *newArray = new int [(size * 2)];

	//Validates that newArray's size will return null if
	//zero or a negative was passed
	if ((size *2) <= 0)
		return NULL;

	//duplicates the contents of the original array into newArray
	for (unsigned index = 0; index < size; ++index) 
		newArray[index] = arr[index];
	
	//assigns a zero to the new elements
	for (int newElem = 10; newElem <(size*2); ++ newElem)
		newArray[newElem] = 0;

	//Returns pointer to the new array
	return newArray;
}

/*******************************************
Function displayArray displays original and 
duplicated array elements
********************************************/
void displayArray (int arr [], int size)
{
	for (int index = 0; index < size; index++)
		cout << arr[index] << " ";
		cout << endl;
}

[Zaita]

The problem is now you've hardcoded 10 at line 66, that should be size

[solemnservant]

oh I see thanks for pointing that out! And thanks for the quick responses!